Metal pickling



252. COMPOSITIONS, F

Patented July 16, 1929.

UNITED STATES Examine PATENT OFFICE.

JAMES H. GRAVELL, OF ELKINS PARK, PENNSYLVANIA, ASSIGNOR TO AMERICAN CHEMICAL PAINT COMPANY, OF AMBLER, PENNSYLVANIA, A CORPORATION OF DELAWARE.

METAL PICKLING.

No Drawing.

This invention relates, generally, to pickling metal, particularly iron and steel, such as defective galvanized work, in a pickle bath, and it consists in the provision of a regulator for causing the acid of the pickling bath to selectively attack unclean portions of metallic surfaces to the exclusion or substantial exclusion of the clean portions of the metal surfaces.

The principal objects of the invention are to prevent the pickle from attacking clean metal, or more accurately, clean portions of the surface of the metal; to avoid the escape of poisonous vapors from the pickle vat; to obviate over-pickling and pitting the Work; to economize in the consumption of acid; to avoid rusting of the pickled work; to reduce the labor of making up pickling baths; to minimize the amount of metal lost in pickling; to cause the pickle to concentrate its energy on the scale removal only; to remove rust and scale from threaded, machined, and polished stock even if of high carbon steel Without mar-ring the finish or altering the dimensions; to provide for the use of a wider range of pickling temperatures; to increase the etliciency of the pickling operation and to prolong the life of the pickling bath; to produce clean work; to speed up the pickling operation; and to keep the atmosphere of the pickling department free from rust forming or promoting elements.

In the art of pickling the metal is treated with dilute acids to remove rust and scale, after which the metal is washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale but unfortunately from the pickling standpoint it attacks the cleaned metal itself, producing an evolution of hydrogen gas which escapes into the air, carrying with it a fine spray of the pickling bath producing an atmosphere of great rusting properties and one which is highly injurious to health. The attack of the pickle on the metal itself not only wastes valuable metal but also uses up the strength of the acid which should be directed to removing the rust and scale.

By the present invention these objectionable features of the pickling process are over' come to such an extent that from a commercial standpoint they can be considered eliminated. To accomplish this in accord- Application filed September 11, 1924. Serial No. 737,068.

ance with my invention I add to the pickling bath a regulating agent or ingredient which acts to restrain the action of the acid in removing the scale and rust, or in other words, it selectively removes the oxides without materially attacking the free metal. Although the regulating or controlling agent acts in this selective manner withother acids, it is especially effective in connection with sulphuric acid, which is the acid generally used for pickling iron and steel.

In order to produce the pickle regulator of my invention, I distill animal or vegetable materials bearing proteid, such as albuminoids, and condense the distillate to secure a liquid containing or constituting a pickle regulator which in association with a pickle bath profoundly alters the action thereof on the work, making the action selective with respect to the surface condition of the metal. The proteid bearing material may, among other things, be hair, gristle, hides, skins, flesh, casein, ossein, gelatine, etc. As a practical example gelatine may be used. This is placed in a still in the regular way. The still is then slowly heated until nothing remains but charred coke, and products of the destructive distillation are collected in a reservoir or condenser in liquid form. A little animal or vegetable fat added to the gelatine before distillation assists in the operation by better distributing the heat throughout the mass and in increasing the yield of control material.

The distillate may be used in toto but I prefer to use the water insoluble portion only because of its superior control action. This insoluble portion apparently consists of a series of basic materials so proportioned as to exert a powerful control effect.

To produce a pickling bath according to my invention, I may use the following formula:

Gallons.

Water 1000.00

Sulphuric acid (66 '13.) 50.00 lVater insoluble portion of distillate .125

distillate may be varied to increase or diminish its control action, and it is evident to those skilled in the art that the amount and kind of acid may be varied to produce a strong or weak bath. An equivalent amount of niter cake or similar acid bearing material can be used to replace the free acid if desired.

The water insoluble distillate dissolves in the acid bath with turbidity and selectively checks the attack of the acid on clean metal, eliminating to a large extent the generation of hydrogen. \Vhat little hydrogen is produced is caught in a blanket of foam produced by the effect of the distillate and held in the foam long enough to deposit all condensed moisture before it escapes to the air, thereby removing all possibilit) of an obnoxious atmosphere such as would cause rust and injure the health. The pickling bath may be used at any desirable temperature from ordinary room temperature up to boiling, as such temperatures have no decomposing effect on the distillate, but as the activity of the acid increases with the temperature of the bath, more distillate should be used as the temperature is increased. The amount of distillate given in the formula is suitable for pickling baths run at approximately 175 F. Generally stated, the amount of distillate required is that which will prevent the visible generation of hydrogen, known commercially as gasing.

The described pickle control or regulator in the pickle bath restrains the action of the acid on free clean metal and therefore greatly diminishes the generation of hydrogen gas which action, in connection with the blanket of foam produced, entirely eliminates the escape of all injurious and rust producing fumes. As my pickle regulator causes practically all attack of the acid to stop as soon as the scale or coating is removed, pitting and over-pickling are reduced, as evidenced by the ability of my pickle bath to remove rust and scale from threaded, polished and machined parts without marring the finish or altering the dimensions. As the acid is prevented from attacking the metal no waste of metal or acid occurs as indicated by tests where a saving of of the acid and 3% of the metal was noted. As acid is not wasted the same pickle bath will pickle a larger quantity of material and, therefore, the bath does not have to be made up so often and hence there results a saving in the labor of making up pickling baths. Heretofore care had to be exercised not to have the pickle too hot or too strong in acid, or both, because there was danger of pitting or over-pickling the metal, but by my invention the temperature and the acid concentration of the bath may be greatly increased in order to diminish the time required for pickling, with less danger of pitting or over-pickling.

It has been noted that steel tubes and other articles treated according to my pickling process resist rusting better than if pickled in the old way where only sulphuric acid is used, and it has also been noted that in drawing tubes pickled according to my invention, a peculiar odor is noted at the dies.

Concentrated sulphuric acid dissolves the distillate.

To those skilled in the art it will be evident that the composition of the distillate constituting the pickle regulator of the present invention is complex, and that the philosophy of its action in causing a pickle bath to act selectively and to remove unclean or oxidized metal surfaces and to spare clean or bright metal surfaces is subject to various explanations, but from the foregoing description thoseskilled in the art will be able to practice the invention, which, for the reasons stated, is not limited to details of procedure, or to the precise ingredients mentioned, or to more matters of form, or otherwise than as the prior art and the appended claims may require under and subject to the range of equivalents appropriate in chemical cases.

I claim:

1. A pickling bath for metals of which one ingredient is a combined pickle regulator and foam producing material, Lsaid ingredient being a distillate from animal bodies.

2. A pickle regulator for selectively controlling the action of metal pickling baths which comprises an admixture of distillate from proteids and strong sulphuric acid in which the distillate is dissolved, thereby producing a regulator to be put into a metal etching batl 3. A pickling bath comprising a metal etching acid and a portion of the distillate of animal bodies which is soluble in strong sulphuric acid and which portion includes a part of the distillate soluble in commercial hydrochloric acid and also the part of the distillate which is not soluble in commercial hydrochloric acid.

JAMES H. GRAVELL. 

